Thwaites glacier (Image from NASA ICE)
Two studies hit headlines (confusingly several media articles reported either one or both of them with similar headlines) this week that suggest that glaciers on the West Antarctic Ice Sheet (WAIS), which was already thought to be vulnerable, are shrinking and are set to contribute significantly to sea level rise.
Map of Antarctica showing the Amundsen Sea, which glaciers of the WAIS flow into.
The outcome isn’t certain: we don’t know enough about Antarctica, it’s history and the Earth’s climate system to really say very much to 100% certainity- but here we have one study that is based on modelling a key glacier on the ice sheet (Thwaites Glacier) and one that is based on observations so the combination of the two provides strong evidence.
The first study models changes in Thwaites Glacier for different levels of melting and for all but the lowest level of melt the onset of rapid collapse of the glacier happens within a millenium (current observations match the higher end of the melting levels they melted, this would have collapse somewhere within the next 300 years or so). The second study is based on observations that several glaciers are melting faster than most scientist had expected.
Thwaites Glacier meeting the ocean (Image NASA ICE).
How much ice are we talking here?
The loss of the whole West Antarctic ice sheet would contirbute 3.3m of sea level rise, and just the glaciers in the 2nd study could contribute over 1.2m between them. However, as mentioned above this is over potentially long time scales but that still doesn’t mean that significant changes could happen, potentially within our lifetimes- these glaciers are already releasing the same amount of ice annually as Greenland.
So why is the WAIS so much at risk?
A simplified diagram of a grounding line (www.AntarcticGlaciers.org).
As the ice shelves coming from the glaciers are melting, they become lighter, meaning that they can float above areas where they used to be grounded. The point where the ice flows off of the land and becomes a floating ice shelf is called the grounding line and the grounding lines of the glaciers studies are moving further back towards the sources of the glaciers.
This retreat can be held back by “pinning points”, hills or bumps beneath the ice- a lack of these and the gerneal shape of the land below the ice reduced that WAIS’s ability to slow the glaciers down.
Bonus extra bit of cool science
You can watch a video by Eric Rignot, author of one of the 2nd study, with lots of exciting graphics and images of what’s underneath the WAIS here:
If this sounds interesting and you’d like a more in depth explanation I’d recommend heading here.
1st study (Joughin et al.): http://www.sciencemag.org/content/344/6185/735
2nd Study (Rignot et al.): http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract
Potential sea level rise from the west Antarctic ice sheet: http://www.sciencemag.org/content/324/5929/901